At autopsy, the hips of six infants who died soon after birth and had
unilateral congenital hip dysplasia were found to have a cartilaginous
ridge in the acetabulum which separated the hip socket into two sections.
In two of the hips with a moderate degree of dysplasia and in one
completely dislocated hip the ridge was formed exclusively by a bulge of
acetabular cartilage. In three completely dislocated hips the ridge was
formed by a bulge of acetabular cartilage covered by the inverted labrum.
The acetabular cartilage showed signs of degeneration whereas the
triradiate cartilage was normal. Examination of many newborn infants
indicated that hip "clicks" are common and are not diagnostic of hip
dysplasia. This diagnosis should be made only when the femoral head slides
with a jolt over the acetabular ridge, causing a true positive Ortolani
sign. Scattered ossification centers in the acetabular cartilage were seen
on the roentgenograms of nearly half of fifty-nine hips with congenital
dislocation reduced after the child was two years old, but less frequently
in hips reduced at an earlier age.